<!DOCTYPE html>
<html>
<body>

<p>Count numbers: <output id="result"></output></p>
<button onclick="startWorker()">Start Worker</button>
<button onclick="stopWorker()">Stop Worker</button>
<br /><br />

<script>
    var w;

    function startWorker()
    {
        if(typeof(Worker)!=="undefined")
        {
            if(typeof(w)=="undefined")
            {
                w=new Worker("demo_workers.js");
            }
            w.onmessage = function (event) {
                document.getElementById("result").innerHTML=event.data;
            };
        }
        else
        {
            document.getElementById("result").innerHTML="Sorry, your browser does not support Web Workers...";
        }
    }

    function stopWorker()
    {
        w.terminate();
    }
</script>

</body>
</html>